How come you can't turn around at a check point? When NYC posted policemen to conduct random searches of bags prior to entering the subway system, you had the right to refuse a search and go on your way, just not onto the subway. Turn around before a police road block, and they go after you.
Remember that if you encounter a DUI checkpoint in the Fort Lauderdale area this holiday season, you can turn around, even if you just want to avoid waiting in the long line of cars at the roadblock.
http://www.floridaduilawyerblog.com/2008/12/dui_checkpoints_in_florida.html